WASHINGTON (Reuters) - U.S. states would be free to decide whether to legalize marijuana without running afoul of federal law but would require purchasers to pay federal taxes on its sale under legislation being proposed by two Democratic lawmakers.

The proposed bills in the House of Representatives aim to offer a new federal policy toward pot, amid a growing movement to legalize it for personal use, whether recreational or medical.

Representatives Earl Blumenauer of Oregon and Jared Polis of Colorado, both Democrats, planned to introduce the legislation on Tuesday.

One bill would end a federal ban on marijuana and give states jurisdiction over its use and regulate it in a similar way to alcohol sales, while the other would levy a federal tax, the congressmen said in a statement.

The Democrats' bills likely face a hurdle in the House where Republicans hold a majority and control what legislation moves forward. A similar, bipartisan effort by other representatives failed to gain traction in 2011.

Washington state and Colorado voted to legalize the drug in 2012 but now face questions on how to implement their laws while U.S. authorities still consider pot illegal. Illinois is also considering acting on the issue.

Eighteen states, including California and Oregon, plus the nation's capital city already allow sales for medical use to help certain patients cope with pain and other chronic conditions, according to the National Conference of State Legislatures, which tracks state laws.

Last year's votes have buoyed those who support easing access to the drug, which U.S. health officials say is the most commonly used illegal drug. Polls show most Americans support legalizing pot.

Critics say that despite widespread use and acceptance, the drug carries health risks, especially for youth. They question whether the drug, derived from the cannabis plant and usually smoked, has benefits for medical use.

Advocates on both sides of the issue are waiting anxiously to see how federal authorities will act as Washington state and Colorado move forward.

The U.S. Justice Department has yet to clarify its stance on the issue, but President Barack Obama has said it does not make sense for the federal government to focus on recreational drug users in such states, given limited government resources and growing public acceptance.

U.S. drug officials have classified marijuana as an illegal drug with no accepted medical use and a high potential for abuse since 1970.